Saturation Bombardment

You can deploy it only in your own watch, while the crossfire is empty, as you deploy a crew: never as a reaction, and not in the sortie phase. Once deployed, it waits in the crossfire like any card, and your opponent can react to it (802.10).

A condition, not a cost: nothing is exhausted. When you deploy it you need two Mechs on board that aren't dispatched, ready or exhausted, new ones too. A crew of yours in a battle doesn't count (306.6).

The opponent is chosen when you deploy it; with one opponent, it is them. Each of their crew in their berth takes the damage as the card resolves; in your watch, that is all of their crew. Plating takes it first, the damage stays, and a crew left with no hull is destroyed at once. Their bases and your own crew aren't hit (705.7g).